Are gibs suppose to move a small amount?

Djstorm100 · Mar 6, 2017

Don't shoot the messenger. I obtain my BP some months back and finally getting around to setting it up. I've seen Keith Ruckers video on how to set gibs and seen Richard's post about it as well. Most of who I talked to said they adjust the gibs by feel. However I do not have anything to compare and say "this is right feel" and "this is wrong". Obviously you can tighten the gibs to night and cause the axis not to move at all, this is obviously wrong. When I've adjusted to where the table gets harder to turn and back of one full turn. However the gibs moves back and forth a small amount (depending on traveling left or right).

Is this normal?

L Vanice · Mar 6, 2017

Tapered gibs have to be restrained from moving, so they have a pair of opposed adjusting screws. If the screws are not tightened, the clearance will change as the direction of travel of the slides changes.

Straight gibs will not change clearance with travel, but most machines do include a means of restraining axial motion to keep the gib in place. The means may be a tight fitting pin through the slide and gib, milled pockets in the gib for dog points on the adjusting screws or sharp points on the adjusting screws. I have seen a thin steel gib with the ends bent over to catch the ends of the slide to keep it in place.

Larry

Monarchist · Mar 6, 2017

Djstorm100 said:
Don't shoot the messenger. I obtain my BP some months back and finally getting around to setting it up. I've seen Keith Ruckers video on how to set gibs and seen Richard's post about it as well. Most of who I talked to said they adjust the gibs by feel. However I do not have anything to compare and say "this is right feel" and "this is wrong". Obviously you can tighten the gibs to night and cause the axis not to move at all, this is obviously wrong. When I've adjusted to where the table gets harder to turn and back of one full turn. However the gibs moves back and forth a small amount (depending on traveling left or right).

Is this normal?

Ideally, they are meant to NOT move. The ideal is never fully possible, if only because of thermals. Then we have wear.

If/as/when an ordinary Mark One human eyeball can readily detect the movement?
It needs to be corrected before it affects the work. Or finds a way to jam the slide.

HOW one corrects it depends on the specific design, but do yer research.

At this late stage, there is No Fine Way you will be the first Pilgrim as ever had the need, any given machine-tool still at-large, not re-melted, and ubiquitous Bee Pee's least of all.

Djstorm100 · Mar 6, 2017

For bridgeport with taper gibs. It moves ever so slightly, if I remember correctly a member said it was to allow oil to lubricate the gib/ways.

Trying to find this post now. If I tighten the gibs to where they don't move then it feels like there is to much drag.

Being new, the last thing I want to do is accelerate the wear.

Edit found it. http://www.practicalmachinist.com/v...-gib-tolerances-operation-328075/#post2878660

amazing I looked for a hour last night and today found the post on the first try.

Monarchist · Mar 6, 2017

Djstorm100 said:
amazing I looked for a hour last night and today found the post on the first try.

Dunno why you should expect to be any different from the rest of us, but yah.. that's how this s**t usually works..

DMF_TomB · Mar 6, 2017

some machine gibs have adjustment screw at each end of gib. i remember trying to tighten a lathe and could not get it tighter. i eventually loosened the opposite end of gib adjustment. then i could push in gib farther so tighter. the opposite gib adjustment screws keep it from moving, somebody might have left one not tighten against gib, thus gib moves a bit on reverse direction
.
some straight non tapered gibs are just screw in a dimple or spot drill hole. might not be tight so gib moves a little on reverse direction. often gib tighter on ends of travel than in the loose middle where more wear is present

Djstorm100 · Mar 6, 2017

But since BP don't have the adjustment screw on both sides, you'll get movement regardless. Even if it's just a little. Visually you can't tell but if you put your finger on the gib you can feel it move.

Danny VanVoorn · Mar 6, 2017

All machines don't have opposing adjustment screws, some have a slot in one end of the gib and a screw that fits it fairly well but nothing on the other end. With that set up the gib can move the amount of clearance but shouldn't be enough for concern. I've seen machines that the last foot of travel would cause a steady US condition visually noticeable on a facing opperation, a simple gib adjustment took care of the problem. I try to tighten the gibs enough to eliminate any movement and leave it at that, no tighter and leave it at that.
Dan

DMF_TomB · Mar 6, 2017

yes some tapered gibs i have seen with screw with big shoulder that engaged slot in side of gib on one end and could push or pull gib
.
slot is normally bigger than screw shoulder. .005 or .050 not sure it really matters although too much movement might cause random tighter and looser feel
.
just saying i tried to adjust gib with screw at front of lathe and had problems for a hour until i looked at the other end and noticed the screw at other end of gib. if you tighten gib it should feel tight, if not most likely there is another gib adjustment screw
.
its rare but sometimes screw will not push gib in farther as its worn too much. but normally they leave a lot of possible adjustment. i have heard of turcite applied to gib that was worn a lot

L Vanice · Mar 6, 2017

Djstorm100 said:
For bridgeport with taper gibs. It moves ever so slightly, if I remember correctly a member said it was to allow oil to lubricate the gib/ways....

The statement you saw meant that you need a tiny clearance between the face of the gib and the face of the moving dovetail to allow room for a lubrication film.

Lengthwise motion of a tapered gib is a bad thing because the gib clearance changes with feed direction. You set the dovetail clearance for the desired value in one direction of travel. Then you measure the clearance in the other direction of travel. If the gib moves, the second measure will be different, tighter or looser, from the first. If the lengthwise movement of the gib is controlled by a single fillister head screw constrained in a mating slot in the gib, then you may need to remachine the worn gib slot and make a new adjusting screw with larger head and tighter thread if the issue becomes a problem. The very long taper of a tapered gib means that some linear motion of the gib makes a much smaller change in clearance, so a loose single screw can usually be ignored. The opposed screws design used on many machines completely eliminates the issue.

Larry

DMF_TomB · Mar 6, 2017

some people like turcite applied as it compresses a bit. ideally always maintaining some gib pressure by expanding and compressing a bit. i have heard it helps absorb vibration chatter

Djstorm100 · Mar 6, 2017

Sounds my interruption of how to adjust gibs correctly was horribly wrong. Wish someone here was near central NC who could show me.

L Vanice · Mar 6, 2017

Djstorm100 said:
Sounds my interruption of how to adjust gibs correctly was horribly wrong. Wish someone here was near central CN who could show me.

I don't think anyone here is near central CN (China). http://apps.cybersource.com/library/documentation/sbc/quickref/countries_alpha_list.pdf

Larry

Djstorm100 · Mar 6, 2017

L Vanice said:
I don't think anyone here is near central CN (China). http://apps.cybersource.com/library/documentation/sbc/quickref/countries_alpha_list.pdf

Larry

Oh come on Larry, you knew I fat finger that..lol

L Vanice · Mar 6, 2017

Djstorm100 said:
Oh come on Larry, you knew I fat finger that..lol

I was just interrupting what you wrote.

Larry

Djstorm100 · Mar 9, 2017

Here are some videos I took in hope you guys could help me out.

Djstorm100 · Mar 9, 2017

Djstorm100 · Mar 9, 2017

onecut · Mar 9, 2017

I would put a foot long bar in my vise and zero the clock in and run it along the bar in both directions.Be honest in my opinion the movement your getting is acceptable I have worked on machines that you could rock the table back and forward with your hand on the table and they cut straight Backlash and Gibb Adjustment on Bridgeport Mill - YouTube

Djstorm100 · Mar 9, 2017

onecut said:
I would put a foot long bar in my vise and zero the clock in and run it along the bar in both directions.Be honest in my opinion the movement your getting is acceptable I have worked on machines that you could rock the table back and forward with your hand on the table and they cut straight Backlash and Gibb Adjustment on Bridgeport Mill - YouTube

It does cut straight. My concern is setting the gibs to tight and causing accelerated wear. I do notice when I'm cutting a smaller pocket out the axis not in use will move .001 or so. It's bugs me as I have a mild OCD problem..LOL

Are gibs suppose to move a small amount?

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